The invention relates to a method of manufacturing a colour display tube, in which a display window is provided with a display screen of phosphor elements luminescing in different colours, a shadow mask having a large number of apertures is suspended in the display window, and an eveloping part is secured to the display window in such a way that an envelope is formed.
Such a method is described in British Patent Specification 2,097,996. In this method pins are provided in the corners of the display window suspension elements are provided at the corners of the shadow mask, and the mask is suspended in the display window by fitting each suspension element on a pin by means of a wire spring.
As is known, the display window is provided with a display screen of phosphor elements luminescing in different colours by a photolithographic process using the shadow mask as a photomask.
In securing the enveloping (cone) part to the display window and during evacuation of the envelope, the envelope is heated to approximately 400.degree. C. During heating the shadow mask expands and it has been found in practice that when the envelope has cooled the shadow mask does not always resume its original position. As a result of this, the apertures in the shadow mask may be displaced relative to the phosphor elements of the display screen leading to colour defects in the colour display tube.